1. Field of the Invention
The present invention relates to electrical interconnections and the electrical contacts for making these interconnections, and, more particularly, to establishing electrical contacts between chip modules or multi-chip modules (MCM) and printed circuit boards (PCBs).
2. Brief Description of Related Developments
The interconnection between a high density multi-chip module (MCM), for example, and a printed circuit board (PCB) typically uses a Ball Grid Array (BGA) or a Land Grid Array (LGA) or a combination of both. These two dimensional arrays provide a plurality of electrical paths between an integrated circuit (IC) package or chip module, a chip carrier, or directly to a chip and a printed circuit board normally positioned in the IC package and under the array. Each electrical path is provided by an electrical contact that is held within an interposer or connector by a variety of techniques. It may be further desired that the connection be non-permanent so that the chip module may be removed for the purpose of upgrading and/or repair such as changing a CPU or adding more memory. In prior LGAs (land grid arrays) connecting ceramic chip modules to boards, a 2D array of springs made from random coils of wire was used. However, the large force required to properly load and actuate the interposer often breaks the expensive chip module.
Another problem with prior art interposers is the loss of restoring force over time rendering the electrical connection vulnerable to failure. This is known to happen with filled elastomer type interconnects and also with metal interconnects due to mechanical wearout mechanisms.
Thus, there exists a need for a LGA connector or interposer that eliminates the stress placed on the IC device upon inserting the IC device into a housing for holding the IC package, and one that does not share the severe loss of restoring force over time exemplified by the filled elastomer type.
In one aspect, the present invention is directed to a method of forming an electrical interconnection between a first electrical device and a second electrical device. In one embodiment, the method comprises providing contacts in an uncompressed state. The uncompressed contacts are then deformed to a compressed state and then the contacts are positioned in a device adapted to hold the contacts between the first and second electrical devices. Alternatively, the uncompressed contacts are positioned in the device and then compressed to the compressed state. The contacts are then activated to substantially expand to the uncompressed state wherein each contact expands to substantially its uncompressed state for establishing the electrical interconnection between the first and second electrical devices.
In another aspect the present invention is directed to a method of forming an electrical connection between a first electrical device and a second electrical device. In one embodiment the method comprises providing contacts composed of a shape memory material. The contacts are deformed to a second position, a compressed state, and then assembled in the compressed state into a device for positioning the contacts between the electrical devices. After the device for positioning is positioned with the contacts in the compressed state between the first and second electrical devices, the contacts are activated to a substantially uncompressed state to make the electrical connection between the first and second electrical devices.
In a further aspect, the present invention is directed to a contact for establishing an electrical connection between a first electronic device and a second electronic device. In one embodiment, the contact comprises a flexible conductive body formed in a first position and adapted to be set into a second position. The contact is activated into a third position in order to accommodate a variable gap between the first electronic device and the second electronic device for establishing the electrical connection.